1. Field of the Invention
The present invention relates to a carburetor and, more particularly, an improvement of a carburetor for use with stratified-charged rotary piston engine with regard to the overall air/fuel ratio performance thereof for effecting a stabilized low speed and low load operation of the engine had a better purification of exhaust gasses.
2. Description of the Prior Art
In the Wankel type rotary piston engine which comprises a casing composed of a rotor housing having a trochoidal inner peripheral surface and side housings which close the opposite ends of the rotor housing, an eccentric shaft, and a polygonal rotor adapted to eccentrically rotate around said eccentric shaft with apex portions thereof sliding over said trochoidal inner peripheral surface, the flame in the combustion chamber initiated by the ignition plug generally propagates very rapidly toward the leading side of the combustion chamber as seen in the rotational direction of the rotor due to a flow of fuel-air mixture generated by the rotation of the rotor, whereas the flame is hard to propagate toward the opposite trailing side of the combustion chamber. Because of this, the fuel-air mixture existing in the trailing region of the combustion chamber is prone to imperfect combustion thereby causing poor fuel comsumption, simultaneously increasing the emission of harmful uncombusted components such as HC and CO.
In order to solve these problems, there has been proposed a new type of stratified-charged rotary piston engine having a first intake port formed as a peripheral port which opens in the trochoidal inner peripheral surface of the rotor housing and a second intake port preferably formed as a side intake port which opens in the flat inside surface of the side housing at a position advanced from said first intake port as seen in the rotational direction of the rotor. The first intake port supplies a relatively rich fuel-air mixture whereas said second port supplies only air thereby ultimately providing a stratified charge in the combustion chamber of the engine in a manner such that the leading side of the combustion chamber is charged with a relatively rich fuel-air mixture while the trailing side thereof is charged substantially with air. This pattern of stratified charging facilities complete combustion of fuel in the combustion chamber and provides an advantage that a higher overall air/fuel ratio can be employed thereby improving the fuel consumption and reducing the emission of harmful uncombusted components. In this connection, there has been proposed a new type of carburetor for use with a stratified-charged rotary piston engine of the aforementioned type, said carburetor comprising a first supply system adapted to supply fuel-air mixture and a second supply system adapted to supply only air, said two supply systems having individual throttle valves operationally co-related with each other to control the total supply of air to the engine. In this case, it has also been proposed to incorporate a special timing mechanism into the linkage co-relating the two throttle valves so that the opening phase of the throttle valve in said second supply system is somewhat delayed from that of the throttle valve in said first supply system, thereby effecting a temporary supply of a richer fuel-air mixture during acceleration of the engine to provide better accelerating performance.
Although a stratified-charge rotary piston engine of the aforementioned type is capable of operating satisfactorily at a normal speed and load operating condition, it still has the problem that operation at a low speed and low load condition (performed by a very small supply of fuel) is prone to become unstable. Furthermore, in a low speed and load operation or idling operation, the exhaust gas temperature substantially lowers and causes a problem that a reactor for purifying uncombusted components such as HC and CO is not maintained in a hot condition required for performing its purification process, thereby causing poor purification efficiency.